Lithium base grease containing group ii divalent metal alkyl salicylate, such as zinc alkyl salicylate, as copper corrosion inhibitor



LITHIUM BASE GREASE CONTAINING GROUP II DIVALENT METAL ALKYL SALICYLATE, SUCH A55 ZINC ALKYL SALICYLATE, AS COPPER CGRRQSION INHIBITOR No Drawing. Application March 4, 1953, Serial No. 340,396

9 Claims. (Cl. 252-36) This invention relates to a lubricating grease composition, and particularly to a lithium base grease which is inhibited against copper corrosion.

Lithium base lubricating grease compositions have found important use in aircraft controls and for other purposes where operation over a wide temperature range, and particularly operation at extremely low temperatures, is encountered. U. S. Patent No. 2,450,221 is typical of a superior lithium base grease of this type prepared from a lithium soap of a hydroxy fatty acid or the glyceride thereof, such as hydrogenated castor oil, and containing as the major proportion of the liquid lubricating base an oil-soluble high molecular Weight high boiling liquid aliphatic dicarboxylic acid ester within the lubricating oil viscosity range and possessing lubricating properties. As disclosed therein, the lithium soap may be formed from a major proportion of the hydroxy fatty acid or glyceride and a minor proportion of a saturated fatty acid, such as for example a 3 :1 mixture of hydrogenated castor oil or l2-hydroxystearic acid with stearic acid. Such greases have exceptional shear and texture stability over a wide temperature range and under high shearing stress, and possess excellent low temperature properties.

While the lithium base greases of the aforesaid type have proved eminently satisfactory in service, the increased use of copper and copper alloys in certain applications, particularly in aircraft and artillery control instruments, has introduced an additional problem of rendering the grease non-corrosive to copper in long time service. For this purpose, U. S. Army Specification 2-134 has prescribed a rigorous copper corrosion test for qualification under this specification. In attempting to meet this specification, it has been found that corrosion inhibitors heretofore employed, in greases are ineffective.

A principal object of the presentinvention is to pro vide a lithium base grease which retains all the desirable properties of the previously known greases of this type, and at the same time is effectively inhibited against corrosion of copper and copper alloys in long time service so as to satisfactorily meet the copper corrosion, test of U. S. Army Specification 2-134.

In accordance with the present invention, it has been found that this object is attained by incorporating in the lithium base grease about 0.25 to 5 per cent, and preferably about 1-3 per cent, by weight of an oil-soluble metal alkyl salicylate of the formula H 0 OH where R is an alkyl radical having from to carbon atoms, n represents the number of hydrogen atoms on the benzene nucleus which have been substituted by R and States Patent is a whole number from 1 to 3, the total number of carbon atoms in the said alkyl substitution on each benzene nucleus being at least 10 and preferably about 18 to 30 or more, and M is a divalent metal of group II of the periodic table selected from the group consisting of zinc, magnesium, barium, calcium and strontium.

The metal alkyl salicylates which are effective copper corrosion inhibitors for purposes of the present invention are preferably prepared from phenol by alkylation with an olefin polymer fraction to produce an alkyl phenol with the desired alkyl substitution on the benzene nucleus; the latter is converted to sodium alkyl phenolate by the sodium methylate procedure; the sodium alkyl phenolate is then carbonated under carbon dioxide pressure and elevated temperature followed by acidification to form alkyl salicylic acid; and the latter is then converted to the group II metal alkyl salicylate by refluxing with an organic solvent, such as xylene, in the presence of a soluble group II metal salt, such as the acetate. The final product is preferably prepared in the form of a concen- Irate in a mineral lubricating oil, such as a 25-50 per cent concentrate. Where a lower molecular weight olefin, such as amylene is used for alkylation of the phenol, the latter is dialkylated or trialkylated to provide a total of at least 10 carbon atoms in the substituent alkyl groups. Where a high molecular weight olefin is employed, such for example as a propylene or butylene polymer fraction having olefins of 18 to 30 carbon atoms in the molecule, the product is generally monoalkylated.

Typical compounds prepared as outlined above and which are useful for purposes of the present invention are zinc alkyl salicylate, wherein each benzene nucleus is mono-alkylated with a C13 to C30 alkyl group, or dialkylated with C5 to C9 alkyl groups; similar compounds of barium, such as barium diamyl salicylate; similar compounds of calcium such as calcium dinonyl salicylate; and similar compounds of magnesium such as magnesium C21 alkyl salicylate. As representative of a preferred compound for purposes of the present invention, the following example of the preparation of a zinc C23 alkyl salicylate is specifically described for purposes of illustration.

An alkyl phenol was selected having an average side chain length of 23 carbon atoms, a hydroxyl number of 136, a calculated molecular weight from the hydroxyl number of 413, with a determined molecular weight of 392. The alkyl phenol had been prepared by alkylating phenol with a proplyene polymer fraction having an average of 23 carbon atoms in the molecule in the pres.- ence of HF as an alkylation catalyst. 2,065 grams (5 mols) of the said C23 alkyl phenol were dried by azeotropic toluene distillation, cooled to C., and grams (5 g.-atoms) of sodium metal were added chunkwise over a one hour period. 700 milliliters of absolute methyl alcohol were added slowly during a four hour period, and reaction of the sodium was completed in about ten hours. Part of the methyl alcohol was removed by condensate trap, and 2,058 grams of a naphthene base lubricating oil having an SUS viscosity at 100 F. of about 300 were then added. The remaining solvents were stripped at C. and 5 mm. mercury absolute pressure to obtain 4,238 grams of a 51.5 per cent lubricating oil concentrate of the sodium C23 alkyl phenolate.

In the manufacture of the alkyl salicylic acid, 1,873 grams of the said concentrate of sodium alkyl phenolate were charged to a bomb which had been flushed several times with CO2. Carbonation was then carried out at 500 pounds per square inch gauge carbon dioxide pressure and at 325 F. for one hour. The resulting bomb product was then diluted with ether, acidified with HCl, and washed until neutral. The product was then dried by benzene azeotropic distillation, and the solvents stripped at 100 C. and 5 mm. mercury absolute pressure to obtain 1,809 grams of product having a neut. No. of 48.6, a calculated concentration in lubricating oil of 64.6 per cent, and a calculated per cent conversion of alkyl phenol to alkyl salicylic acid of 71.5 per cent. 1,800 grams of this product were then recarbonated under the following conditions. 203 grams (3.58 mols) of sodium methoxide were added slowly to the product in solution in 1.5 liters of dry toluene at room temperature. Then 400 milliliters of absolute methyl alcohol were added slowly and stirring continued until sodium methoxide disappeared, indicating its reaction with acidic and phenolic hydroxyl groups of the product. The solvents were then stripped at 130 C. and mm. mercury absolute pressure, and carbonation was repeated under the same conditions as set forth above. 84 grams of additional lubricating oil were added to bring the product to 50 per cent concentration. 1,772 grams of final product were obtained having a neut. No. of 63.4, which calculated to complete conversion of the C23 alkyl phenol to C23 alkyl salicylic acid.

In the preparation of the zinc salt, 1,350 grains (1.5 mols) of the C2 alkyl salicylic acid (approximately 50 per cent concentration in lubricating oil) were stirred together with 165 grams (0.75 mol) of zinc acetate in refluxing xylene. The refluxing was continued until liters of the solvent were removed by trap and until the product no longer showed an acidic reaction to indicator paper. The remaining xylene was then stripped off under vacuum. 1,273 grams of additional mineral lubricating oil were then added to obtain a per cent concentrate. 2,546 grams of final product were obtained, which was a viscous liquid analyzing 2.20 per cent ash against a theoretical ash content of 2.07, and 1.74 per cent zinc against a theoretical content of 1.66 per cent zinc, for a 25 per cent concentrate of zinc C23 alkyl salicylate.

The above described group H metal alkyl salicylates may be employed in lithium base greases formed from any saturated fatty material, such as the conventional saturated fatty acids or glycerides thereof, to provide copper corrosion inhibition.

Preferably, the lithium base greases formed from hydroxy fatty acids or their corresponding glycerides, such as hydrogenated castor oil, are employed to obtain the improved shear and texture stability. Suitable types of soap forming hydroxy fatty acids and glycerides thereof are disclosed in said Patent No. 2,450,221. While the soap forming hydroxy fatty acids or their glycerides may be used as the sole acidic component of the lithium soap, they may be blended or combined with the conventional saturated fatty acids in such proportions that at least per cent of the total acidic component is composed of the hydroxy fatty acids or glycerides thereof. Very satisfactory results are secured by employing as the saturated fatty material for the formation of the lithium soap a mixture of about -80 per cent by weight of hydrogenated castor oil or 12-hydroxystearic acid, with 40-20 per cent of a saturated fatty acid such as stearic acid. The grease may contain about 10-30 per cent by weight of the lithium soap.

In order to obtain the improved wide temperature range and low temperature properties, the liquid lubricating base of the lithium grease composition is preferably formed of a major proportion of a synthetic oleaginous lubricating compound or condensation product, many types of which are now known in the art. Very satisfactory synthetic lubricants of this character are represented by the high molecular weight high boiling liquid aliphatic dicarboxylic acid esters which are within the lubricating oil viscosity range and possess lubricating properties. The compounds within this particular class are the esters of such acids as sebacic, adipic, pimelic, azelaeic, alkenyl succinic, alkyl maleic, etc. The esters thereof are preferably the aliphatic esters and particularly the branched chain aliphatic diesters. Specific examples of the preferred oleaginous compounds are di-2- ethylhexyl sebacate, di-Z-ethylhexyl azelate, di-Z-ethylhexyl adipate, di-isooctyl adipate, di-secondary amyl sebacate, di-2-ethylhexyl alkenyl succinate, di-Z-ethoxy ethyl sebacate, di-2-(2-methoxy ethoxy) ethyl sebacate, di-2-(2-ethyl butoxy) ethyl sebacate, di-2-butoxy ethyl azelate, di-2-(2'-butoxy ethoxy) ethyl alkenyl succinate, etc.

These oleaginous compounds may be used as the sole oil component of the grease or they may be blended with a mineral lubricating oil. Where a blend is employed, and low temperature properties are required, the mineral lubricating oil is preferably a light refined distillate mineral lubricating oil, such as a naphthene or paraifin base distillate, having an SUS viscosity at 100 F. of about 50-130 and preferably about 100 seconds. The mineral lubricating oil will generally constitute less than 50 per cent of the blend, and ordinarily about 40-5 per cent thereof. The mineral lubricating oil blend is advantageous where the lithium soap is formed in situ. in such cases, the saponification of the fatty material with the lithium hydroxide and dehydration of the resulting soap are conveniently carried out in the presenc e\ 1 of the mineral lubricating oil or a portion thereof, and the synthetic lubricant together with the additives employed in the grease are then added following dehydration and as the agitated soap mix cools.

An example of a preferred type of grease of this character consists essentially of the following constituents in the approximate percentages by weight:

Di-isooctyl adipate 50-85 Lithium soap of a 2:1 to 4:1 weight mixture of hydrogenated castor oil and stearic acid 10-30 Phenyl alphanaphthylamine 3.0-1.0 Metal alkyl salicylate as defined above 0.5-3.0 Mineral lubricating oil Balance Di-isooctyl adipate; .Q. 50-75 Lithium soap of a 2:1 to a 4:1 Weight mixture of hydrogenated castor oil and stearic acid 12-25 Phenyl alphanaphthylamine 0.3-1.0 Dibenzyl disulfide 0.5-3.0 Sorbitan monooleate 1.0-4.0 Zinc alkyl salicylate as defined above 0.5-3.0

The following specific example is given to illustrate the present invention. A lithium base grease was prepared from a fatty material consisting of about per cent by weight of hydrogenated castor oil and 25 per cent by weight of stearic acid. The lubricating base used was a mixture of about 75 per cent by weight of diisooctyl adipate with about 25 per cent by weight of a parafiin base mineral lubricating oil having an SUS viscosity at F. of about 100. The method of preparation involved charging a steam heated kettle with the required amount of 10.3 per cent of lithium hydroxide solution together with a small amount of water, the hydrogenated castor oil and a proportion of the paraflin base mineral lubricating oil, the latter being less than the amount of hydrogenated castor oil and generally about one-half to two-thirds of the latter. The kettle contents were held at -200 F. for about four hours with agitation, and then the stearic acid was added and Mineral lubricating oil the temperature maintained with stirring for another 1-2 hours to complete saponification. Following saponification, a per cent concentrate of an octyl methacrylate ester polymer in a mineral lubricating oil, which is sold commercially by Rohm and Haas under the name Acryloid HF-600, was added in an amount to provide 1.9 per cent by weight of the concentrate or approximately 0.5 per cent by weight of the active polymer in the final grease composition.

The saponified mix was then heated with stirring at 290 to 330 F. for about four hours to effect dehydration. The balance of the mineral lubricating oil was then added with stirring as the kettle contents cooled down to below 280 F. The di-isooctyl adipate was then slowly added with stirring as the mix continued to cool to about 220 F. Phenyl alphanaphthylamine in an amount of 0.5 per cent by weight based on the grease was added as an oxidation inhibitor, together with l per cent by weight of dibenzyl disulfide and 2 per cent by weight of sorbitan monooleate and a small amount of a dye. The resulting base grease was drawn at a temperature below 200 F.

The resulting base grease had the following calculated composition:

Weight per cent Lithium soap of hydrogenated castor oil 12.2 Lithium stearate 4.3 Excess LiOH 0.2

Glycerine (from saponification of hydrogenated castor oil) 1.2 Paraffin base lubricating oil 19.2 Di-isooctyl adipate 57.5 Sorbitan monooleate 2.0 Dibenzyl disulfide 1.0 Acryloid HF-600 1.9 Phenyl alphanaphthylamine 0.5 Dye 0.0026

To separate portions of the foregoing base grease, amounts of the above described zinc C23 alkyl salicylate were added to provide 1 per cent and 3 per cent by weight based on the total grease composition respectively. The said greases were then subjected to the copper corrosion test of the 2-134 specification, in comparison with the base grease, with the results as shown in the following table:

copper corrosion inhibitors. which are effective in other relationships are completely ineffective for purposes of the present invention. As shown by samples 2 and 3 of the foregoing table, the zinc alkyl salicylate was surprisingly effective in enabling the grease to pass this rigorous copper corrosion test. While materials of this general character have heretofore been proposed as detergent additives for lubricating oils, such as motor oils, it was entirely unexpected that these particular group II metal alkyl salicylates as above defined should be effective as a copper corrosion inhibitor in the new environment of a lithium base grease.

While the additives of the present invention have been specifically described above in connection with lithium ba'se greases because these are representative of the type generally employed for specialty wide temperature range service, and particularly low temperature service, it is to, be understood that the invention is not limited thereto. Rather, the invention is also applicable to the improvement of the copper corrosion properties of other metal base greases, including those of sodium, calcium, barium, and mixed base greases, wherein the soap formingfatty material of the metal soap consists of at least per cent by weight of hydroxy fatty acid or the glyceride thereof, such as l2-hydroxystearic acid and hydrogenated castor oil. For example, a grease comprising an oleaginous liquid lubricating base, such as a mineral lubricating oil or a synthetic lubricant base or mixture thereof, thickened to a grease-like consistency with about 10-30 per cent of calcium IZ-hydroxystearate, may have added thereto. for copper corrosion inhibition about 0.25-5 per cent by weight of a metal alkyl salicylate of the type described above.

Obviously many modifications and variations of the 5 invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and there fore only such limitations should be imposed as are indi: cated in the appended claims.

We claim:

1. A lubricating grease composition comprising as, the essential constituents an oleaginous liquid lubricating base of which at least the major proportion is a liquid aliphatic dicarboxylic acid ester within the lubricating viscosity range, about 1030% by Weight of a lithium soap of a TABLE 2-134 Cu Corrosion Test Additive Wt. Percent Rating gjig Copper Grease 1. Base Grease Brown stain Rust colored-- Fail" 0 2. Base Grease+1% Zinc 02; No change; slight do Pass; border- 0 alkyl salicylate. brown stain in dupline.

licate test. 3. Base Grease+3% Zinc C2; Nochange d0 Pass 0 alkyl salicylate.

The 2-134 corrosion test of the foregoing table was run by placing a copper strip in a Norma Hofimann bomb so as to be partially immersed in the sample of the grease under test, and then maintaining the bomb under oxygen pressure (110 pounds per square inch initial pressure) at 210 F. for 20 hours. During that period no pressure drop due to oxygen absorption must occur. Then, at the completion of the 20 hour period, both the sample of grease and copper strip are inspected. There must be no more than a very faint stain on the copper strip and no more than a slight stain or discoloration on the grease in order to be rated as passing.

As will be noted from the foregoing table, even the base grease which contained 0.5 per cent by weight of phenyl alphanaphthylamine, an effective oxidation inhibitor, showed no pressure drop in the test, indicating that the copper corrosion which resulted with the base grease is not attributable to normal oxidation. Likewise, and as set forth in U. S. Patent No. 2,610,946, recognized saturated soap-forming fatty material, said grease normally being corrosive to copper, and from 0.25 to 5% by weight based on said composition of an oil-soluble metal alkyl salicylate of the formula enable said grease composition to pass the copper corrosion test of U. S. Army Specification 2-134.

2. A lubricating grease composition according to claim 1, wherein said salicylate is a C1s-C3o alkyl salicylate.

3. A lubricating grease composition according to claim 1, wherein said salicylate is a zinc alkyl salicylate.

4. A lubricating grease composition consisting essentially of the following constituents in the approximate percentages by weight:

Di-isooctyl adipate 50-85 Lithium soap of a 2:1 to 4:1 weight mixture of hydrogenated castor oil and stearic acid 10-30 Phenyl alphanaphthylamine 0.3-1.0 Metal alkyl salicylate as defined in claim 1 0.5-3.0 Mineral lubricating oil Balance 5. A lubricating grease composition according to claim 3, wherein said salicylate is zinc C18-C30 mono-alkyl salicylate.

6. A lubricating grease composition consisting essentially of the following constituents in the approximate percentages by weight:

Di-isooctyl adipate 50-75 Lithium soap of a 2:1 to 4:1 weight mixture of hydrogenated castor oil and stearic acid 12-25 Phenyl alphanaphthylamine 0.3-1.0 Dibenzyl disulfide 0.5-3.0 Sorbitan monooleate 1.0-4.0 Zinc alkyl salicylate as defined in claim 3 0.5-3.0 Mineral lubricating oil 5-35 7. A lubricating grease composition comprising as the essential and at least major proportion of the lubricating base an oil soluble high molecular weight high boiling liquid aliphatic dicarboxylic acid ester within the lubricating viscosity range and possessing lubricating properties, sufiicient lithium soap or soap-forming fatty material to thicken said lubricant base to a grease consistency, said soap-forming fatty material consisting of more than 50 per cent by weight of a hydroxy soap-forming fatty material selected from the group consisting of hydroxy fatty acids and hydroxy faty acid glycerides, and from 0.5 to 3 per cent by weight based on said composition of an oil soluble metal alkyl salicylate of the formula on J on -o--M-o b where R is an alkyl radical having from to 30 carbon atoms, n represents the number of hydrogen atoms on the benzene nucleus which have been substituted by R and is a whole number from 1 to 3, the total number of carbon atoms in the said alkyl substitution on each benzene 7 consisting of sebacic, azelaeic and adipic acids, with said diester being in major proportion of said mixture, about 10-30 per cent by weight based on the composition of lithium soap of a mixture of a major proportion of hydrogenated castor oil and a minor proportion of stearic acid, and from 0.5 to 3 per cent by weight based on said composition of an oil soluble metal alkyl salicylate of the formula where R is an alkyl radical having from 5 to carbon atoms, 11 represents the number of hydrogen atoms on the benzene nucleus which have been substituted by R and is a Whole number from 1 to 3, the total number of carbon atoms in the said alkyl substitution on each benzene nucleus being at least 10, and M is a divalent metal of group II of the periodic table selected from the group consisting of zinc, magnesium, barium, calcium and stroii u M tium, said salicylate being in sufiicient proportion to enable said grease composition to pass the copper corrosion test of U. S. Army Specification 2-134.

9. A lubricating grease composition comprising as the essential constituents an oleaginous liquid lubricating base of which at least the major proportion is a liquid aliphatic dicarboxylic acid ester within the lubricating viscosity range, about 10-30 per cent by weight based on said composition of a metal soap of a soap-forming fatty material, said soap-forming fatty material consisting of at least per cent by weight of a hydroxy fatty material selected from the group consisting of hydroxy fatty acids and the glycerides thereof, said grease being normally corrosive to copper, and from 0.25 to 5 per cent by Weight based on said composition of an oil soluble metal alkyl salicylate of the formula where R is an alkyl radical having from 5 to 30 carbon atoms, n represents the number of hydrogen atoms on the benzene nucleus which have been substituted by R and is a Whole number from 1 to 3, the total number of carbon atoms in the said alkyl substitution on each benzene nucleus being at least 10, and M is a divalent metal of group II of the periodic table selected from the group consisting of zinc, magnesium, barium, calicum and strontium, said salicylate being in sufficient proportion to enable said grease composition to pass the copper corrosion test of U. S. Army Specification 2-134.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A LUBRICATING GREASE COMPOSITION COMPRISING AS THE ESSENTIAL CONTITUENTS AN OLEAGINOUS LIQUID LUBRICATING BASE OF WHICH AT LEAST THE MAJOR PROPORTION IS A LIQUID ALIPHATIC DICARBOXYLIC ACID ESTER WITHIN THE LUBRICATING VISCOSITY RANGE, ABOUT 10-30% BY WEIGHT OF A LITHIUM SOAP OF A SATURATED SOAP-FORMING FATTY MATERIAL, SAID GREASE NORMALLY BEING CORROSIVE TO COPPER. AND FROM 0.25 TO 5% BY WEIGHT BASED ON SAID COMPOSITION OF AN OIL-SOLUBLE METAL ALKYL SALICYLATE OF THE FORMULA 